Preparation of dehydrogenation catalysts



Patented Feb. I, 1949 ATENT OFFICE PREPARATION OF DEHYDROGENATION CATALYSTS John George Mackay Bremner, Peter William I Reynolds, andArthur William Charles Taylor, Norton-on-lees, Eng-land, assignors to Imperial Chemical Industri vlion of Great Britain No Drawing. Original a Serial No. 398,680, n August 14, 1945. Div July 28, 1945, Serial No. 607,650.

Britain June 21, .1940

6 Claims.

This invention relates to dehydrogenation cat- 7 .lysts include, for, example, that of impregnating activated alumina, c. g. in the .form .of porous calcined granules, with .achromic acid solution.

These known catalystswhen :used for example in .the dehydrogenation of para-bin Lhydrocarbcns to the corresponding olefines, deteriorate in activity and have carbonaceous material depositedon themdurin the dehydrogenation, but they can be regenerated by interrupting the dehydrogenation process and passing an ,OXYEGIP- containing gas over themat an elevated temper- .ature.

In practice, therefore, the dehydrogenation is carried out in a series of cycles of alternating periods of dehydrogenation and regeneration.

The decrease in activity which occurs from the moment when dehydrogenation is commenced to the moment when it is interrupted and regeneration started, is hereinafter termed intracy- .clic deterioration.

'We have found that when these known catalysts are used "for many cycles of dehydrogenation and regeneration, a decrease in the mean activity in each hydrogenation period gradually becomes evident. therefore, does not fully restore the activity of those known catalysts. 'The degree of "restoration obtained "by the regeneration process decreases with increase 'in'temperature of the dehydrogenation and-the regeneration.

We have now'found a catalyst which for any given temperature of dehydrogenation and regeneration can be more completely regenerated than the known catalysts can be under the same conditions, 'and'which moreover, when employed at temperatures of the-order of 500 C. to 600 C. 'doesnot showanyappreciable tall in mean activity :per cycle, -;in two *months of continuous subjection to alternate cycles of dehydrogenationand regeneration.

The regeneration process,

es Limited, a corporapplication alone 18, 1941, ow Patent No. 2,382,394, ided and this application in Great The catalyst of the present invention'comprises as its essential constituent, a product obtained by cautious thermal decomposition of a precipitate produced from an aqueous solution containing an aluminium salt, together with ammonium chromate, ammonium dichromate, .or chromium triOXlde by adding thereto :ammonia,

ammonium bicarbonate, or ammonium carbonate in an amount atleast sufiicient to give substantially complete precipitation of the aluminium.

Aluminium nitrate has been found to be a convenient aluminium salt for use in the'prep aration of the catalyst. Any soluble aluminium salt may, however, be'used, e. g., aluminiumchlo- .ride or its hydrated forms, or aluminium sulphate.

The .ratioof'aluminium salt to the ammonium .dichromate, ammonium chromate, or chromium trioxide, may be varied within wide limits. It

is preferred to use aratio of aluminium salt to chromium -.compound such that the chromium content, reckoncdas CrzOs, of the saidessential constituent on a water-free basis is between 40% and 50%.

Aluminiumsaltsfrequently contain iron which, unless it is poisoned by sulphur, increases the deposition of carbonaceous material on the catalyst whenit is .used forthe .dehydrogenationof organic compounds. When .a solution of alu- .miniumsalt and ammonium .diohromate is employed, itis therefore advantageous to allowthe solution to standfor .a few hours, when-the bulk of any iron ,ipresent settles out as ferric dichromate and can'be separated from the solution, be-

;fore the addition of ammonia or its carbonate not applicable when ammonium chromate is used, since in solution it reacts immediately with the aluminium salt to give a precipitate of alu= minium hydroxide.

of precipitating agent does not appear to be critical, but it is preferred to add just suflicient to obtain substantially complete precipitation.

The precipitate, after separation from the mother liquor, should not be subjected to any extensive washing and in general it is desirable that the precipitate should not be washed at all.

The precipitate is conveniently dried at room temperature in air or in an oven at a temperature up to about 120 C. and then disintegrated before subjecting it to thermal decomposition.

The thermal decomposition of the precipitate is carried out by heating it slightly in order to start the reaction, and then continuing to heat carefully until the reaction is substantially complete. In view of the exothermal nature of the decomposition, care should be taken to avoid the development of high local temperatures, for example, by suitable disposition or agitation of the precipitate. It appears that the decomposition should take place at as low a temperature as possible for the best results. The decomposition is conveniently carried out in air, but other atmospheres, such as steam, nitrogen or hydrogen, may be used.

We have further found that intracyclic deterioration of the catalyst and carbonaceous deposition can be decreased by the presence in the catalyst of a compound of the alkali metals or the chromite, chromate, or dichromate of zinc.

The chromates of the alkali metals have been found to be better than other alkali metal compounds, and the compounds of zinc hereinbefore mentioned. Potassium compounds in general appear to give better results than the corresponding compounds of the other alkali metals and potassium chromate is outstandingly better than all other compounds tested.

In the early stages of the life of a catalyst containing potassium chromate, carbon deposition is very small and intracyclic deterioration is almost absent. On prolonged subjection to alternate cycles of dehydrogenation and regeneration, carbon deposition increases to a limiting value, and intracyclic deterioration appears, but both are lower than for a catalyst containing no potassium chromate.

In general the alkali metal compounds should be present in an amount by weight between 0.05% and 5.0% of the product obtained by the thermal decomposition hereinbefore described. The corresponding percentages in the case of the zinc compounds in general lie between 0.05% and 10.0%.

The alkali metal and zinc compounds may be introduced into the catalyst in any suitable manner, e. g., by addition as such or by production in situ, and at any convenient stage in or after the manufacture of the essential constituent of the catalyst. We prefer, however, to mix the alkali metal and zinc compounds with the previously prepared essential constituent, make the mixture into a slurry with water, and finally d y it.

The catalysts of this invention may have incorporated in them other compounds such as the oxides of magnesium, aluminium, and zinc,

and may be used supported on suitable carriers or in the form of granules or as pellets.

The activity of the catalysts of this invention is influenced by the amount present in the material to be hydrogenated. For any given raw material, the amounts of water which are suitable can easily be determined by a few simple experiments.

As examples of dehydrogenation processes for which our catalysts are useful, there may be cited the dehydrogenation of hydrocarbons such as the conversion of paraffin hydrocarbons to olefines containing the same number of carbon atoms, and the production of diolefines from olefines.

The following examples are given to illustrate the preparation of the catalysts of this invention, and their use in the dehydrogenation of paraffin hydrocarbons.

Example 1 A catalyst was prepared by adding a solution of 1 part by weight of ammonium dichromate in 4.5 parts by weight of water to a solution of 2 parts by weight of aluminium nitrate (A1(NO3)3.9H20) in 2.6 parts by weight of water. The mixed solutions were heated to -C. and precipitated by the addition of 1.1 parts by weight of aqueous ammonia containing 25% by weight of NIH, the mixture being thoroughly stirred throughout and for 10 minutes after the addition. After cooling to room temperature, the precipitate was filtered, pressed and dried at C.

The dried precipitate was powdered and cautiously decomposed by heating it in small portions in a porcelain dish over a low flame, the powder being vigorously stirred to prevent excessive heating by bursts of spontaneous decomposition. The highly exothermic decomposition began at about C. and was substantially completed by raising the temperature of the powder to 350 C. The material was finally heated in dry air to 500 C., maintained at this temperature for 1 hour, and cooled.

The powdered catalyst prepared in the manner described, was mixed with 4% by weight of aluminium stearate and pelleted to x cylinders. These were finally calcined in air up to 500 C. to remove the organic material of the pelleting lubricant.

15 ccs. of this pelleted catalyst were charged to a silica reaction tube filled on each side of the catalyst with silica chips, and heated in a suitable furnace to 540 C. A mixture of 80% isobutane and 20% n-butane was dried over fused calcium chloride and admitted to the catalyst at a space velocity of 2000 litres (measured at 20 C. and 1 atmosphere) per litre of catalyst space per hour. The run was continued for hour, and a mean sample of the exit gas collected. At the end of this time the system was purged for 2 minutes with nitrogen at a rate of 5000 litres (measured at 20 C. and 1 atmosphere) of nitrogen per litre of catalyst space per hour, regenerated with calcium chloride-dried air-for 25 minutes at reaction temperature and the same space velocity as with nitrogen, purged again with nitrogen, and the cycle of operation recommenced. This cycle of operation was continued for 2 months, the reaction temperature being increased from 540 C. to 580 C. and brought back again'to 540 C. at the conclusion of the run.

The results obtained are shown in the following table, from which it is apparent that the acitivity of the catalyst had not diminished apof water vapour enomes F5 preciably after 2' months processing. nt'thetend of the run the catalyst removed .zfrom the apparatus andwas found to be scarcely inferior in pellet strength to their-ash material. 'L'Ihe butylene yield throughout the -run"- was "greater than 95 =Averege per- Catalyst gcent butylene No. of Cycles Temperature in mean t5 inC. hour exitgas :sample 1st-50th c. 540,, 16. 100th-l50th--. 550 17. 7 150th-200th 550 "17.6 200th-250th. 1-5'55 18.1 .250th-300th- 560 19. 9 300th-350th 560 19. 3 400th450th i 570 i 20.0 450th500th 570 20.9 500th'550th 570 20. 5 5S0th-600th, :570 3 519.5 650th-700th- 580 21. 6 '700th-750th. 580 21.3 800th-850th 57.5 v22.2 850th-900th 575 I 21. 5 sooth-950th 575 21.8 Q50th-1000th. 4575 I 20.8 l000th-1050th 575 ;2l.9 1050th'1120th 570 1 21:7 1120th-12ooth-. 57o 20.8 mouth-127mm. 570 20. .7 1'270th1360th. 570 '20. 1 l350th-1400th 540 15.?

Example 2 A powdered catalyst was prepared as described inliExample .landthe powder mixed to a paste with .2. /e% of itsweightof potassium .chromate dissolved in water. The ,paste was dried and pelleted with the addition of. 4% of valuminium stearateasa binder.

Substantially pure propane, dried .over'calcium chloride, waspassed at the rate of .2000volumes of propane (measured at C. andl atmosphere) per unit volume of catalyst space per hour, over the .catalyst maintained at a temperature of 620 C. and samples of the exit gas were taken over hourly periods. During the hourfollowing the first 15 minutes of the run the average olefine and hydrogen contents of'the exit gas were respectively 17.5% and 18.0%. following the first 1 /2 hours of the run the average olefine and hydrogen contents of the exit gas were respectively16.7% -a.-nd1'i;0%. During the hour following the first 4 hours of the .run the average olefine and hydrogen contents of the exit gas were respectively 129% and 135 In a comparative experimenta catalyst prepared exactly as above but without the-addition of potassium chromate was charged in the iorm of pelletsinto the reaction vessel, and substantially-pure propane, dried over calcium chloride, was passed over it at the rate of 2000 volumes of propane per unit volume of catalyst space per hour, the temperature of the catalyst being 620 C. during the hour following the first 15 minutes of the run the average olefine and hydrogen contents of the exit gas were respectively 17.9% and 17.5%. During the hour following the first 1%; hours of the run the average olefine and hydrogen contents of the exit gas were respectively 12.2% and 11.6%. The marked efiect of potassium chromate in suppressing intracyclic deterioration of the catalyst of the invention is apparent from these results.

powder obtained as described in Example 1, an

equal weight of powdered magnesia, mixing the constituents thoroughly by light grinding and During the hour dried at 110 ri'lnallypelletingmththe addition of4% by weight 'or almninium stearate.

Substantially pure propane, dried by passage over fused calcium chloride, was passed over this sample of the exit gas taken over the first 1% hours of the run contained 15.3% hydrogen and 14.5% olefines, of Which more than was "propylene.

Example 4 Apowdered catalyst'was prepared as described in-Exarnple 1. Aportionof this powderedmaterial'wasi made into cylindrical pellets 4; long, %"--diameter, after the addition of 4% of aluminium stearate to act as a lubricant and binding. agent. Another portion of this powdered material was mixed with 1% by weight of potassium chromatein the presence of a little water, C. and made into cylindrical pellets, 24; long, diameter, after the additionof 4% .oi-aluminium stearate to act as a lubricant and bindingagent. The two products were calcined in-air-at 500 C. to remove the organic-material of the pelleting agent.

1000s. each of these catalysts were filled into silica reaction tubes in a furnace block at 620 C. and propane dried over calcium chloride admitted to the tubes at a space velocity of 2000 litres (measured at 20 C. and 1 atmosphere) per litre of catalyst space per hour. Samples for anaylsis were takcn'from the exit gases over a period of 2' hours, at' the end of Which the catalyst was. regenerated by heatingior 1 hour in air. The carbonremovedfrom the catalyst during regeneration was determined.

. Several cycles ofdehydrogenation and catalyst regeneration werecarried out and the following results were obtained.

"Mean Per centConversion Carbon removed in regenof .Propanedur ng 2-hour oration. Weight of car- '(ichydro'genation period hon/cubic metre propylone formed .Qyclc Catalyst Catalyst Catalyst Catalyst without with 1% without with 1% potassium potassium potassium potassium chromatc chromate chromate eliminate Example 5 A powdered catalyst was prepared as described in Example 1. Four samples from one batch of this material were taken. The first was mixed with 4% by weight of aluminium stearate and pelleted. The remaining samples were mixed with 1%, 2% and 5% by weight respectively of zinc chromate, slurried with a little water, dried at C. admixed with 4% by weight of aluminium stearate and pelleted. The four catalysts were tested together in the dehydrogenation of propane which had been dried over calcium chloride. The dehydrogenation was carried out at 620 C. and a space velocity of 2000 litres of propane (measured at 20 C. and 1 atmosphere) per litre of catalyst space per hour. After 50 hours processing on propane with intermittent air regeneration at reaction temperature, the olefine content of the exit gas collected over a half-hour dehydrogenation period and the corresponding carbon deposition in the catalysts were as follows:

Gms. Carbon We claim:

1. A process for the preparation of a dehydrogenation catalyst comprising adding to an aqueous solution containing an aluminium salt and a compound selected from the group consisting of: ammonium dichromate, ammonium chromate, chromium trioxide, a precipitant selected from the group consisting of: ammonia, ammonium bicarbonate, ammonium carbonate in an amount at least sufficient to give substantially complete precipitation of the aluminium, separatin the resulting precipitate from the mother liquor, drying it in unwashed state at a temperature below 120 C., subjecting the dried product in powdered form and in small portions to vigorous stirring and careful heating at about 120 C. in order to thermally decompose it, and then adding to the decomposed product from between 0.05% and based on its weight, of potassium chromate.

2. A process as claimed in claim 1 characterised in that when thermal decomposition is substantially complete, the product is heated in air to a temperature of about 500 C.

3. A process for the preparation of a dehydrogenation catalyst comprising preparing an aqueous solution containing an aluminium salt and ammonium dichromate, allowing the solution to stand, separating the solution from any ferric dichromate impurity which settles out, adding to the solution a precipitant selected from the group consisting of ammonium bicarbonate, ammonium carbonate in an amount at least sufiicient to give substantially complete precipitation of the aluminium, separating the precipitate from the mother liquor, drying the unwashed precipitate at a temperature not exceedin 120 0., subjecting it to cautious thermal decomposition, and then adding from between 0.05% and 5% by weight of the thermally decomposed product of a compound selected from the group consisting of potassium chromate, sodium chromate, zinc chromite, zinc chromate, and zinc dichromate.

4. A process for catalyst manufacture which comprises forming an aqueous solution containing an aluminum salt and a compound selected from the group consisting of ammonium dichromate, ammonium chromate, and chromium trioxide, adding. to said solution, in an amount at least sufiioient to substantially completely precipitate the aluminum, a precipitant selected from the group consisting of ammonia, ammonium bicarbonate, and ammonium carbonate, subjecting the resultant precipitate after recovery from its mother liquor and in substantially unwashed state to cautious thermal decomposition, and incorporating in the decomposed product between 0.05 and 5% by weight of a compound selected from the group consisting of potassium chromate, sodium chromate, zinc chromite, zinc chromate, and zinc dichromate.

5. The process of claim 4 characterized in that the solution contains a ratio of aluminum salt to chromium compound such that the chromium content of said product, on a water-free basis and calculated by weight as chromium sesquioxide, is between and 6. A process for the manufacture of catalysts suitable for use in hydrocarbon dehydrogenation, which comprises forming an aqueous solution containing an aluminum salt and a compound selected from the group consisting of ammonium dichromate, ammonium chromate, and chromium trioxide, adding to said solution, in an amount at least sufficient to substantially completely precipitate the aluminum, a precipitant selected from the group consisting of ammonia, ammonium bicarbonate, and ammonium carbonate, subjecting the resultant precipitate after recov-- cry from its mother liquor and in unwashed state to cautious thermal decomposition and incorporating in the decomposed product from 0.05% to 5% by weight of a compound selected from the group consisting of potassium chromate, sodium chromate, zinc chromite, zinc chromate, and zinc dichromate.

JOHN GEORGE MACKAY BREMNER.

PETER WILLIAM REYNOLDS.

ARTHUR WILLIAM CHARLES TAYLOR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,184,235 Groll et al Dec. 19, 1939 2,205,140 Heard (II) June 18, 1940 2,205,141 Heard (I) June 18, 1940 2,216,262 Bloch et a1 Oct. 1, 1940 2,249,337 Visser et al. (II) July 15, 1941 2,271,751 Visser et al. (I) Feb. 3, 1942 2,294,414 Matuszak et al. Sept. 1, 1942 

